Tape alignment apparatus

ABSTRACT

Means are disclosed herein for determining alignment between recorded data tracks carried on magnetic tape and playback heads employed to detect the data. An endless loop of a test tape is driven past the playback head so that the dimensional distance between the top edge of the tape and the top of the playback head can be measured against microscopic scale. Should the distance be other than that set for proper playback tracking, the playback head may be vertically adjusted to compensate for any misalignment.

United States Patent [72] Inventor Nicholas P. Trist 7580 San FernandoRoad, Sun Valley, Calif. 91352 [21] Appl. No. 768,734 [22] Filed Oct.18, 1968 [45] Patented June 1, 1971 [54] TAPE ALIGNMENT APPARATUS 6Claims, 17 Drawing Figs.

[52] 11.8. C1. 356/172, 274/4 [51] Int. Cl. G011: 11/26 [50] Field ofSearch... 356/172, 156,247, 253, 165, 166; 350/81; 242/55.19; 274/4 [56]References Cited UNITED STATES PATENTS 2,247,] 13

6/ l 941 Benford 2,557,029 6/1951 Grifi'in 256/172X 2,574,712 11/1951Sachtleben 256/172X 3,285,526 11/1966 Moore 242/55.19 3,423,039 1/1969Zielke 242/55.19 3,463,594 8/1969 Myer 356/172 Primary Examiner-RonaldL. Wibert Assistant Examiner-T. Major Attorney- Roger A. Marrs ABSTRACT:Means are disclosed herein for determining alignment between recordeddata tracks carried on magnetic tape and playback heads employed todetect the data. An endless loop of a test tape is driven past theplayback head so that the dimensional distance between the top edge ofthe tape and the top of the playback head can be measured againstmicroscopic scale. Should the distance be other than that set for properplayback tracking, the playback head may be vertically adjusted tocompensate for any misalignment.

saw u or 4 MIG/40445 P. Te/sr IN VEN TOR.

TAPE ALIGNMENT APPARATUS BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to the field of test instrumentationand more particularly to a novel magnetic tape alignment apparatusadapted to test and check alignment of a plurality of recorded magneticsignal tracks with respect to the playback head employed to sense thesignals in each of the tracks.

2. Brief Description of the Prior Art In recent years, magnetic taperecording has improved vastly in providing high density packing ofrecorded information of a fixed length of magnetic tape. Thisimprovement has occurred most markedly in the field ofprerecordedmusical selections carried on the tape in parallel tracks.Originally, single track tape was employed followed by two track, fourtrack and currently, eight track recordings. The number of tracks hascaused each of the tracks to be recorded in closer proximity to adjacenttracks as the overall number of tracks has increased. Since a playbackhead is employed to detect the magnetic signals present in each track,it is obvious that the playback head must be properly aligned with thetrack being sensed so that none of the recorded information is lost.

High density packing of the magnetic signals may cause cross-talkbetween adjacent tracks if the playback head is not properly alignedwith the track or tracks being sensed. Particularly in musicalrecording, a sufficient number of frequencies are lost due tomisalignment of the playback head'with respect to the track beingdetected. Therefore, the setting of playback head azimuth in relation tothe tracks and hence the tape per se is critical.

Conventionally, tape recorders preset playback head azimuth at thefactory so that proper'alignment is attained.

However, repeated 'use of the equipment generates vibration alignment isdifficult to detect and even when detected,

resetting of the playback head is a precise procedure in order to assurerequired accuracy. Therefore, a need has existed to provide a means forchecking the alignment of the playback head with a plurality of magneticrecorded tracks carried on a tape and for measuring the amount ofmisalignment, if any, so that head azimuth may be reset.

SUMMARY OF THE INVENTION Accordingly, the problems and difficultiesencountered with playback head alignment are obviated by the presentinvention which provides a cartridge carrying an endless loop of testtape adapted to be driven past an opening'formed in one end of thecartridge in close proximity to the recorder playback head. The testtape is driven by conventional tape drive means carried in the recorderwhich operates directly on the tape via a powered drive roller. Amicroscope is adjustably mounted on the cartridge havingan optical axisthat includes the portionof the test tape at the cartridge opening andthe top of the playback head. A scale is provided in the microscope lenssystem whereby the distance between the top edge of the tape and the topof the playback head may be accurately measured in terms of thousandthsof an inch. Any discrepancy in measurement between actual playback headazimuth and factory setting may be determined and playback headadjustment may be made to reset the head, if necessary.

Furthermore, means are provided forilluminating' the optical axis sothat the scale and comparison of the tape and playback head positionscan be clearly observed. The intensity of the illumination is adjustablefor optimum tape tracking pattern viewing.

Therefore, it is among the primary objects of the present invention toprovide a novel device for determining playback head azimuth indicativeof head misalignment with prerecorded magnetic information disposed in aplurality of 1 tracks on a prerecorded tape.

Another object of the present invention is to provide a novel magnetictape and playback head alignment sensing device that will readilydetermine proper playback head azimuth with respect to the tape in orderto avoid the cross-talk and frequency loss of prerecorded magneticsignals on the tape.

Another object of the present invention is to provide a test instrumentincluding a microscope having a graduated scale in its lens systemoperably to measure the distance between the top of the playback headand the top edge of a test tape to determine proper alignment orthepresence of any misalignment therebetween from preset positions.

Yet another object of the present invention is to provide a novel devicewhich enables a person to visually determine the alignment of magnetictape in an eight-track stereo tape cartridge playback unit by means of acalibrated microscope so that proper adjustments in the playback-unitmay be made for alignment.

Still another object of the present invention is to provide a novel testinstrument used for the purpose of eliminating cross-talk" andmaintaining playback head azimuth adjustment in eight-track cartridgeplayback units.

Yet a further object of the present invention is to provide a novel testinstrument carrying an endless loop of test tape and a calibratedmicroscope that may be employed to check tape playback head tracking andwhich may be employed for averaging playback head adjustment mechanismerrors such as, for example, averting out cam lobe errors.

BRIEF DESCRIPTION OF DRAWINGS tion with the accompanying drawingswherein like numerals I designate like parts in the several figures.

FIG. I is an enlarged diagrammatic view of a typical magnetic tapehaving eight recorded tracks and illustrating the alternate positions ofthe playback head with respect to selected programs;

FIG. 1a is a diagrammatic view of the topedge of the tape and the top ofthe playback head as viewed through the microscope incorporated in thepresent invention;

FIG. 2 is a perspective view of the tape alignment apparatus of thepresent invention illustrated preparatory to installation with aconventional magnetic tape playback recorder;

FIG. 3 is a perspective view of a microscope suitable for use in thetape alignment apparatus shown in FIG. 2;

FIG. 4 is a top plan view of the tape alignment apparatus installed inthe playback recorder and illustrated with portions thereof broken awayto show the component parts thereof;

FIG. 5 is a cross-sectional view of the microscope vertical and lateraladjustment means employed in the apparatus shown in FIG. '4 as taken inthe direction of arrows 5-5 thereof;

FIG. 6 is a cross-sectional view of the microscope mounting means astaken in the direction of arrows 6-6 of FIG. 4;

FIG. 7 is a fragmentary sectional view of the playback head verticaladjustment means employed in the recorder of FIG. 4 as taken in thedirection of arrows 7-7 thereof;

FIG. 8 is a side elevational view of another embodiment of the presentinvention for use in connection with magnetic tape storage on areel-to-reel arrangement;

FIG. 9 is a top plan view of the tape alignment apparatus employed inthe embodiment shown in FIG. 8;

FIG. 10 is an enlarged perspective view of. the tape align.- mentapparatus shown in FIGS. 8 and 9;

FIG. 11 is a cross-sectional view of the apparatus shown in FIG. 10 astaken in the direction of arrows 1 1-11 thereof;

FIG. 12 is a cross-sectional view of the apparatus as taken in thedirection of arrows 12-12 of FIG. 11;

FIG. 13 is a perspective view of still another embodiment of the presentinvention constituting a simplified version of the apparatus shown inFIG. 2;

FIG. 14 is a cross-sectional view of the apparatus shown in FIG. 13illustrating the components parts thereof;

FIG. 15 is a sectional view of the apparatus case illustrating themicroscope mounting as taken in the direction of arrows 15-15 ofFIG. l4;and

FIG. 16 is a sectional view of the apparatus case illustrating the tapetension means shown in FIG. 14 as taken in the direction of arrows 16-16thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an enlargedportion of a typical magnetic recording tape is indicated by the numeralthat carries a plurality of magnetically recorded signals in a pluralityof parallel tracks identified by the numerals 1-8 inclusive. In allstereo recordings, at least a pair of tracks are employed for a signalprogram. Therefore, program one" is represented by track I and track 5,program "two" by track 2 and track 6, program "three" by track 3 andtrack 7 and program four" by track 4 and track 8. A playback device 11includes a playback head 12 and a second playback head 13 which arearranged in fixed spaced apart relationship such that the spaceinbetween covers two tracks on the tape. Therefore, for each program ofthe four programs, the playback device 11 will align heads 12 and 13with two selected magnetic signal tracks carried on the tape. Thisalignment is shown in FIG. 1 wherein the heads 1 and 2, corresponding toheads 12 and 13, respectively, are shown in solid lines for program one"and in broken lines for the other three programs.

The tape moves in either of the direction indicated by the error 14 soas to move the recorded information in the selected program tracksacross the pair of playback head 12 and 13. However, when it is desiredto change from one program to another, the playback device 11 is movedin a vertical direction in accordance with arrows 15 so that a new setof recorded tracks are selected for a new program. The means for drivingthe tape in accordance with arrow 14 or for vertically positioning theplayback device 11 in accordance with arrow 15 are conventionalmechanisms normally employed in a tape recorder unit and therefore neednot be described in further detail.

To understand and appreciate the criticality of magnetic playback headalignment with selected tracks, the following dimensional information isprovided which is conventional in the preparation and construction ofmagnetic tapes and tape recorders. For example, playback head 12 extendsapproximately 0.002 of an inch above the top edge of the tape in programone" position and approximately 0.01 I of an inch separates the positionof the heads from one track to another. The distance between tracks onthe tape taken from their centerline location is approximately 0.033 ofan inch and the overall width of the tape is approximately 0.247 of aninch. The width of each playback head 12 and 13 is approximately 0.022of an inch and the distance between the heads taken from theircenterline is approximately 0.132 of an inch. Therefore, it can be seenthat the alignment of the centerline of heads 12 and 13 is extremelycritical with respect to the pair of tracks for each of the fourprograms. Tape tracking by the playback heads must be in properalignment in order that the playback heads detect or sense the magneticsignals carried in each of the tracks whereby crosstalk of frequencyloss is either nonexistent or greatly reduced.

Referring now in detail to FIG. 2, the tape alignment apparatus of thepresent invention is illustrated in the direction of arrow 16 whichtakes the form of a test tape cartridge including a rectangular baseportion 17 having a central opening 18 and a forward portion 20 havingchamfered corners 21 and 22 in a manner similar to a conventional tapecartridge. The forward portion 20 is adapted to be insertably receivedinto an opening 23 formed in a forward wall 24 of a tape recorderplayback unit or apparatus 25. The central opening 18 in the base 17 isadapted to removably receive a microscope 26 having an eyepiece 27carried on one end of a tube 30 in order to accommodate viewing by theuser. The tubes 28 and 30 are carried on the main body or housing of themicroscope 26 and may take the form of any conventional microscopeincluding lens system having suitable optical magnification.

The base portion 17 further includes a channel 31 interconnecting thecentral opening 18 with a corresponding and coextensive channel 32formed in the forward portion 20. The channel 31 is adapted to receivetube 30 of the microscope so that the microscope may be mounted on thebase by means of mountings 33 and 34 which will be described later. Itis to be noted that the channel 32 in the forward portion includes anopening 35 in the rear wall thereof which lies on the optical axis ofthe microscope coaxially with tube 30.

In order to provide power for illumination means employed in the presentinvention, a taped transformer power pack 36 is employed having amanually operated dial 37 for adjusting the intensity of the light orillumination. The power back 36 is coupled to the base 17 by means of acable 38 while a cable 40 connects the power pack to AC line voltage.However, if desired, a power cable 41 having an adapter coupler 42carried on one end thereof, may be employed for detachable coupling withthe cigarette lighter in an automobile when it is desired to use theinvention in connection with tape recorder equipment installed in anautomobile.

Inasmuch as the apparatus 16 is intended to be mounted through slot 23on the recorder 25, a substantial portion of the apparatus will becantilevered outwardly from the front panel 24. In order to support thefree end of the apparatus so that the forward portion within the slot 23is in proper position to check alignment of the playback heads 12 and13, a pair of extendable legs 43 and 44 are slidably carried on the endof base 17. Once the apparatus has been installed in the recorder, screwfasteners 45 may be loosened so that the legs 43 and 44 will self-locateon a supporting surface, such as a table, bench or the like, after whichthe screw fasteners 45 are tightened to releasably secure the legs intheir self-located positions. These legs will give support to theapparatus so that it will not wobble or tilt with respect to the opening23.

Referring now in detail to FIG. 3, the microscope 26 is illustrated asbeing detached from the base 17 and it is further illustrated that thetube 28 is angularly disposed with respect to tube 30 so as toaccommodate convenient viewing through the eyepiece 27. Inasmuch as thelens system and optical magnifying means are not a part of the presentinvention, it is to be understood that a suitable magnifying lens systemis employed which is of conventional design.

Referring now in detail to FIG. 4, it can be seen that an endless loopof test tape '50 is movably carried on the front portion 20 and the base17 about rear idler rollers 51 and 52, front idler roller 53 and anidler-driven roller 54. The endless loop of test tape 50 is tensioned bymeans ofa sliding block 55 movably carried within a slotted recess 56formed in the end of base 17 and which is operated by means of a knurledknob 57 in threadable contact with the block via a threaded shank 58.The block 55 carries a pair of rollers 60 pressing against the tape 50.Inasmuch as the rollers 60 engage the tape between the idlers 51 and 52,the tape may be tensioned as the block 55 moves rectilinearly within therecess 56. More or less tension upon the tape is provided by thisadjustment.

The opposite end of the apparatus illustrates that the forward portion20 is provided with openings adapted to receive a drive roller 61adapted-to engage against the tape 50 in driving relationship therewithand an aperture or opening for receiving the playback device I 1. Whenthe playback device is inserted through the opening, the heads 12 and 13come into contact with the tape 50. Suitable stops and electrical switchcontacts taking the form of elements 62 and 63 are employed in aconventional manner to limit the travel of the cartridge forward portion20 in the slot 23 and to complete an electrical circuit causing thedevice roller 61 to be power driven.

The playback device 11 is projecting outwardly from a mount 64 whichincludes a downwardly projecting pin 65. The free end of the pin 65 camsagainst a step-level disc member 66 which is rotatably carried via ashaft 67. As shown in FIG.

7, the member 66 includes step-levels 68, 70 and 71. Therefore, theplayback device 11 may be vertically adjusted in its azimuth elevationfor program selection by rotating the disc member 66 so that the pin 65rests on a selected step-level. Such a device for selecting playbackhead azimuth is conventional to one skilled in the art and does not forma part of the present invention. By threadably mounting the pin 65 onthe mount 64,head azimuth may be adjusted in microscopic increments of athousandths or even a millionths of an inch. The pin may be rotated withrespect to the mount of manually turning the pin with a screwdriver orother suitable tool so that the free end of the point bears against themember 66 to raise or lower the playback heads.

It can be seen that the playback device 11 carrying the playback heads12 and 13 is disposed through the central opening at the end of frontportion in coextensive alignment with the opening 35 and the microscope26. Thus, the portion of tape 50 moving across the playback device 11 isexposed to viewing through the microscope so that physical observationof the tape with respect to the playback heads can be had. To provideproper illumination for such observation, a pair of lamps 70 and 72 aresuitably mounted on the forward portion 20 and are connected to a powercoupling 73 to which power cable 38 is detachably connected. In FIG. 1a,a typical view of the playback head and tape dimensional relationship isillustrated through the eyepiece 27. A graduated scale 74 is provided inthe lens system of the microscope and is preferably graduated in unitsof thousandths of an inch so that the top of the head 12 may be measuredwith respect to the top edge of tape 50. If misalignment is observed,the user may adjust the playback head azimuth as previously describedwith respect to the positioning of point 65.

The microscope 26 is mounted on the base 17 so that tube 30 resideswithin channel 32 by means of a centering ring 75 through whichthe tube30 is disposed in engaging relationship. The centering ring 75 ismounted between a pair of opposing pins 76 and 77 which pivotally engageagainst the opposite sides of the centering ring 75. As seen moreclearly in FIG. 6, the pins 76 and 77 are in threadable engagement withthe body of base 17 whereby rotation of the pin will cause the ring andhence, the tube 30 to be adjusted laterally in a horizontal plane, ifdesired. Also, it can be seen that a cover 78 is carried on the body ofthe base 17 so as to enclose lateral channels 80 and 81 adapted to guideand accommodate portions of the endless tape loop.

The microscope is further supported by means of mounting 34 whichincludes a yoke 82 rotatably supporting a knob 83 for moving a threadedshank 84 into engagement with the tube 30. This relationship is moreclearly illustrated in FIG. 5 wherein the opposite side of tube 30 fromits side engaged by shank 34 is seated upon a resiliently biased pinelement 85. By this mans, rotation of knob 83 will adjust the verticalaxis of tube 30. Furthermore, lateral adjustment of the tube may beachieved by rotation of a wheel 86 having a pin 87 engageable with aside of the tube 30 while its opposite side is engaged by a resilientlybiased pin element 88.

Therefore, it can be seen that the optical axis of the microscope may bereadily adjusted vertically and horizontally by means of adjustmentknobs 83 and 86in a universal manner. Such adjustments permit improvedobservation by the viewer and ensures an adequate and accurate viewingof the top of the tape'edge and the top of the head 12 for determiningalignment parameters.

Referring now to F 16$. 8 and 9, another embodiment of the presentinvention is illustrated within the tape alignment apparatus isillustrated in the general direction of arrow 100. The apparatus ismounted on a side panel 101 of a tape recorder 102 having a pair ofreels 103 and 104. The recorder 102 is commonly known in the art as areel-to-reel tape system in which reel 103 is a supply reel for storinga length of magnetic tape 105 in a coil or roll and wherein reel 104 isa pickup reel for drawing tape from the storage reel 103. During thetransfer of tape from reel 103 to reel 104, a portion of the tape istrained past a playback unit 106 including the playback head for sensingthe recorded information on the magnetic tape.

The apparatus includes a microscope 107 similar to the microscope shownin FIG. 3 which is carried on a collar 108 secured to an upstandingbracket 110. The bracket 110 includes a right-angled flange 111 which isadjustably secured to a support bracket 112 by means of fasteners 113.The support bracket 112 includes a downwardly depending portion 114which is secured to the recorder wall 101.

Referring now in detail to FIG. 10, it can be seen that the collar 108mounts the forward tube of the magnifying microscope 107 by means of auniversal member 115 that may take the form of a ball adjustably mountedin an interference fit with the spherical walls of a bore 116. Theright-angled flange 11 1 is adjustably supported on the support bracket112 by means of a pair of slots 1 l7 and 1 18 formed in the flange inspaced parallel relationship. Each of the slots accommodates a fastener113 which, when tightened, secures the flange 111 to the supportbracket.

It is also to be noted that the support bracket portion 114 includes apair of slots and 121 which are arranged in parallel on the oppositeedge marginal regions of the portion 114. These latter slots areemployed to slidably mount a pair of hook or clamp members 122 and 123,respectively, adapted to engage over the top edge of panel 101 formounting purposes. The pair of hook members are carried on a backplate124 which includes a pin 125 slidably positionable within a slot 126 forguiding purposes. Slot 126 is located midway between the opposite sidesof portion 114 and is formed in the portion between slots 120 and 121.

In FIG. 11, the attachment means including hook member 123 and backplate 124 are illustrated wherein the hook member is carried by theplate by means of adjusting screws 127 and 128. By this means, the hookmembers may be readily adjusted to conform to the contour of panel 101when it is desired to mount the apparatus 100 onto the recorder 102.Each of the screw members 127 and 128 are in threadable engagement withthe plate 124 so that when the screw are rotated, the clamp member 123may be securely coupled to the panel.

FIG. 12 illustrates that pin 125 may take the form of the head of awingnut fastener 130 which bears against the back side of the backplate124 when tightened. By this means, the backplate carrying the clampmembers 122 and 123 may be vertically adjusted with respect to thesupporting bracket portion 114.

Therefore, it can be seen that the microscope 100 may be suitablymounted on collar 108 within bore 116 so that its optical axis may bedirected to view the tape alignment with respect to the playback heads.For precise adjustment, the bracket 110 may be suitably adjusted bymeans of fasteners 113 and the support bracket 112 may be readilyadjusted to properly seat against front panel 101 by the adjustmentscrews 127 and 128. The observation of tape alignment with respect tothe playback heads is identical to the procedure described with respectto the apparatus as shown in FIGS. 2-7.

With reference to FIG. 13, another embodiment of the present inventionis shown in the general direction of arrow 200. The apparatus includes acase 201 substantially similar to a conventional tape cartridgeincluding chamfered corners 202 and 203, respectively, formed in its endadapted to be inserted into the slot of a recorder. Furthermore, thecartridge case includes notches 204 and 205 disposed in similarlocations as notches provided on a conventional tape cartridge tofacilitate releasably locking and securement of the cartridge case in aconventional recorder. One end of the case provides an opening 206through which a tube 207 projects exteriorly of the case so as topresent an eyepiece 208 suitable for observing tape alignment.

As shown in FIG. 14, the tube 207 is an image magnifying device, such asa microscope, which includes a lenssystem incorporating eyepiece 208 anda magnifying lens 209. The magnifying lens 209 includes a scale similarto the scale 74 shown in FIG. la. The magnifying tube 207 is carried onthe case by means of a clamp block 210 and is secured to the case bymeans of screw fasteners 211 and 212 as shown in FIG. 15. Preferably,the clamp block is in two parts having hemispherical opposing surfaceswhich clamp about the periphery of the tube 207.

A test tape 213 is trained about idier rollers 214 and 215 as well as acorner idler 216. It is to be noted that the front portion of the case201 includes an opening 217 so as to permit a playback unit carryingplayback heads to be placed into engagement with the test tape 223 andan opening 218 is adapted to receive a drive roller for engagement wiihthe test tape in order to drive the test tape. A tape guide 220 isemployed which comprises a cantilevered wire adapted to slidably engagewith the top edge of the tape 213 as the tape is moved by the recorderdrive rolier so as to direct the tape portion immediately ahead of themicroscope out of the field of view. Tape 213 is tensioned by means of acontraction spring 221 hooked at one end to the case 201 and hooked atits opposite end to a pivotal plate 222 carried on the case by pivotalconnection 223. The idler roiier 214 is rotatably mounted on plate 222and therefore, the test tape is maintained relatively taut because ofthe contracting tension of spring 221 urging the plate to rotatecounterclockwise about a pivot 223. However, it is to be understood thatthe tension is yieldable so that the tape is not so rigid that it willbreak when the playback head is moved into contact therewith throughopening 217. FIG. 16 more clearly shows the pivotal plate 222 secured onthe case by pivot connection 223.

Inasmuch as the case 201 encloses the microscope 207, a suitableillumination means 224 is carried on the inside of the case within amounting cylinder 225. The cylinder is openended so as to throwsufficient illumination from the lamp bulb onto the tape portion andrecorder playback head within the field of observation. The bui'o forthe illumination means 224 is connected by suitable wires to a powercoupling 226 which may be supplied from battery, line power or the like.

The apparatus 20%) shown in FIGS. 13-16 inclusive represents an economicand simplified version of the apparatus shown in FIGS. 27. The opening217 is in alignment with the optical axis of the microscope 207 so thatthe top edge of the test tape 213 may be dimensionally compared with thetop of the playback head carried on the recorder within ihe opening 217.Inasmuch as tape 213 is endless and travels in front of the microscopelens 209, it is to be noted that the spring guide 220 is placed on topof the tape so as to guide the tape beneath the viewing area of themicroscope so that only the top tape edge portion between the rollers216 and 215 appears through the eyepiece 208. This relationship ispermitted by mounting the idler roller 214 on plate 222 so that theroller 215 is lower in elevation than the idler 214. Therefore, the tapemust travel from a lower elevation from idler 215 to a slightly elevatedroller 214.

In view of the foregoing, it can be seen that the apparatus embodimentshown in FIGS. 2 and 13 provide a configuration similar to standard tapecartridges so as to be accepted into conventional recorders. Theapparatus cartridges are equipped with transparent tape, rollers and atapeway which simulate the tape action in a standard cartridge. The tapeis put into motion by means of the driving mechanism carried in therecorder unit and the user may then view the tape tracking patternthrough the microscope.

With respect to the embodiment shown in FIG. 2, light intensityadjustment may be made by rotating the knob 37 on the power pack unit 36while the microscope may be focused by sliding the microscope backwardsor forward on the base. Rotary knobs 83 and 86 are employed to centerthe microscope on the desired viewing area. Knob 83 is empioyed toadjust the microscope up and down while knob 86 is used to adjust theside-to-side motion of the scope. For best results, it is desirable toequal out the head overlap between head 1, track 1, program one and head2, track 8, program four. This dimension is normally 0.002 inch 0.001inch above and below the tape. Playback head azimuth may be reset afterobserving the tape edge by setting heads 12 or 13 parallel to the tape.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

Iclaim:

1. An alignment test apparatus for determining dimensional displacementof a playback head mounted in a tape recorder comprising:

a cartridge having a pair of adjacent openings formed in a selected endthereof for insertably receiving the playback head and the tape driveroller of the recorder when the apparatus is inserted in said recorder;

an endless loop of test tape threaded in an endless path within saidcartridge to move past said pair of cartridge openings;

a plurality of idler wheels rotatably mounted in said cartridge withinthe loop formed by said endless tape and being in frictional supportingcontact with said tape;

a plate rotatably supporting a. selected one of said idler wheels andbeing pivotally mounted in said cartridge;

a contracting spring yieldably connected between said cartridge and saidplate so as to normaiiy bias said plate to tension said tape via saidselected idler wheel;

a microscope means mounted on said cartridge having an optical axis inalignment with a selected opening when occupied by the playback head soas to establish a field of view including a portion of said tape and theplayback head;

illumination means enclosed within said cartridge for illuminating saidfield of view; and

a lens system carried in said microscope and having a graduated scalelocated on said optical axis thereof.

2. The invention as defined in claim 1 including means carried on saidcartridge slidably engageable with a first portion of said tape looplying between said microscope and the playback head so as tosubstantially direct said portion away from said optical axis while asecond portion of said tape loop passes across the playback head.

3. The invention as defined in claim 1 wherein said cartridge includes abase portion opposite said selected end having a central openingcommunicating with an elongated channel for supporting said microscope.

4. The invention as defined in claim 3 including adjustable legs carriedon the end of said case opposite to its end insertably receiving theplayback head for supporting and stabilizing said base portion when saidcase is installed in the tape recorder.

5. The invention as defined in claim 3 including a universal meansinterconnecting said microscope with said base portion within saidchannel for movably supporting said microscope whereby said optical axismay be selectively moved.

6. The invention as defined in claim 3 including means connected to saidilluminating means for adjusting the intensity of illumination emanatingtherefrom in said field of view.

1. An alignment test apparatus for determining dimensional displacementof a playback head mounted in a tape recorder comprising: a cartridgehaving a pair of adjacent openings formed in a selected end thereof forinsertably receiving the playback head and the tape drive roller of therecorder when the apparatus is inserted in said recorder; an endlessloop of test tape threaded in an endless path within said cartridge tomove past said pair of cartridge openings; a plurality of idler wheelsrotatably mounted in said cartridge within the loop formed by saidendless tape and being in frictional supporting contact with said tape;a plate rotatably supporting a selected one of said idler wheels andbeing pivotally mounted in said cartridge; a contracting springyieldably connected between said cartridge and said plate so as tonormally bias said plate to tension said tape via said selected idlerwheel; a microscope means mounted on said cartridge having an opticalaxis in alignment with a selected opening when occupied by the playbackhead so as to establish a field of view including a portion of said tapeand the playback head; illumination means enclosed within said cartridgefor illuminating said field of view; and a lens system carried in saidmicroscope and having a graduated scale located on said optical axisthereof.
 2. The invention as defined in claim 1 including means carriedon said cartridge slidably engageable with a first portion of said tapeloop lying between said microscope and the playback head so as tosubstantially direct said portion away from said optical axis while asecond portion of said tape loop passes across the playback head.
 3. Theinvention as defined in claim 1 wherein said cartridge includes a baseportion opposite said selected end having a central openingcommunicating with an elongated channel for supporting said microscope.4. The invention as defined in claim 3 including adjustable legs carriedon the end of said case opposite to its end insertably receiving theplayback head for supporting and stabilizing said base portion when saidcase is installed in the tape recorder.
 5. The invention as defined inclaim 3 including a universal means interconnecting said microscope withsaid base portion within said channel for movably supporting saidmicroscope whereby said optical axis may be selectively moved.
 6. Theinvention as defined in claim 3 including means connected to saidilluminating means for adjusting the intensity of illumination emanatingtherefrom in said field of view.